Yeah same, as much as I love Traffic ++ it kills my loading times. Having the UK building themes was nice but again it was taking 2-3mins to load up via an SSD. Most of my mods change the gameplay mechanics more than the look.
I used to love using the Traffic++ mod but it really does slow down my game as the city grows. There has been discussion of that mod and one or two others joining to make a modular super type mod. Unless the lag issues are sorted I'll have to just avoid using it.
I gave up with the UK building theme, just updated with lights as well, as I agree the impact on performance as the city grew was too severe.
The mods I'm currently using...
Time Warp
Power Relay
Multi Track Station Enabler
City Vitals Watch
Daylights Classic
Night time Solar Power
Enhanced Zoom
Cloud and Fog Toggler
Auto Line Color
Unlock Basic Roads
IPT
All 25 Areas
One Way Street Arrows
Chirp Filter
Road Color Changer
Transport Lines Manager
European Buildings Unlocker
Mod Achievement Enabler
Toggle Traffic Lights
^^^ Quite a few that I enjoy using which enhance my enjoyment. Thankfully, unlike assets and themes etc, they don't seem to slow the game down much.
I do have a few assets which are pre made grids of roads etc which can be dropped and interlocked together to make shaped districts etc without too much effort.